Foamed materials are currently used as seal materials in various fields such as civil engineering, architecture, electrics, electronics, and vehicles. Examples of the foamed materials used as such seal materials include thermoplastic resin foams comprising resins such as polyethylene-based resins and polypropylene-based resins, and rubber foams comprising rubbers such as synthetic and natural rubbers.
Of the seal materials, water-resistant seal materials are used for filling clearances of various structures such as buildings, electric devices, and vehicles to prevent water infiltration into the structures. The water-resistant seal material is placed at a portion to be sealed in its compressed state, and repulsion force generated by shape recovery from its compressed state allows the seal material to closely adhere to the interface of the sealed portion without a clearance.
In the case where the water-resistant seal material has low flexibility against compression, the water-resistant seal material generates too high repulsion force, resulting in deformation of the sealed portion. The deformation of the sealed portion causes expansion of the clearance of the structure. This results in decrease in adherence (hereinafter, referred to as sealability) of the water-resistant seal material to the sealed portion, thereby causing insufficient water resistance.
Accordingly, open-cell foamed materials are used as the water-resistant seal materials as the open-cell foamed materials have excellent flexibility against compression. On the other hand, the open-cell foamed material contains cells communicating with one another. This causes easy infiltration of water into the foamed material, resulting in poor water resistance. In the case where the open-cell foamed material absorbs water to swell and thereby achieves higher sealability, the open-cell foamed material has poor sealability until it sufficiently absorbs water, and thus, the open-cell foamed material allows water to infiltrate therein before achieving sufficient sealability.
Foamed materials having both closed cells and open cells are also used as the water-resistant seal materials. In such foamed materials, the closed cells contribute to good water resistance, and the open cells contribute to good flexibility against compression. For example, Patent Document 1 discloses a shaped seal material which comprises a foamed structure. The foamed structure contains both closed cells and open cells, and cell membranes absorb water to swell. The shaped seal material contains eight or more cells per 1 cm in length.
Disadvantageously, the repulsion force of the shaped seal material deteriorates when the shaped seal material is used for a long time. This causes reduction in sealability and results in insufficient water resistance.
Foamed materials used as water-resistant seal materials generally contain additives such as flame retardants, antioxidants, and pigments for improving their properties such as flame-retardant properties and weather resistance, for preventing oxidation and thermal degradation, and for coloring. Almost all of these additives are in a powder state, and the foamed material containing powdery additives generates heavy load upon kneading in the production. This causes poor productivity.
In the case where the foamed material contains the powdery additives, the powdery additives emerge on the surface of the material. This causes reduction in sealability and results in insufficient water resistance.
Patent Document 1: Japanese Kokai Publication H09-111899 (JP-A H09-111899)